Densification systems generally have two broad goals. The first goal is to reduce the volume of a certain material to facilitate its transportation. The second goal is to normalize the shape and size of the densified product, called briquettes, to facilitate its handling and often to make it compatible with mechanized handling equipment.
In the case of biomass and waste material destined for energy production, an additional goal of the densification is to improve the combustion or gasification of the material, by generating fuel briquettes of a certain size, shape and density. For example a pile of wood sawdust does not burn very well, but a briquette made of the same sawdust can make an excellent solid fuel.
The densification of biomass and waste material is somewhat more difficult to achieve than the densification of inert or inorganic material such as metal chips. This is because biomass and waste material are heterogeneous mixtures and the successful generation of briquettes with this material is influenced by its composition, moisture content and particle size distribution. Presses designed for the densification of biomass and waste material have certain characteristics in order to reliably process these materials into briquettes.
Biomass briquettes made of woody fibers generally fall in three categories: logs (or ingots), pucks and pellets. Fuel ingots vary in diameter from 50 mm to 100 mm, and are usually 60 mm to 150 mm long. They are generally used as a cleaner and more consistent alternative to residential firewood logs, offering a higher energy density and steady combustion. Fuel pucks have similar diameters to ingots but can be 25 mm to 50 mm in length. Fuel pucks are used in co-firing coal-powered electric generation as well as in institutional heating, greenhouse heating, and combined heat and power (CHP) applications. Fuel pellets are smaller cylinders usually with a 6 mm to 8 mm diameter and with a length that is variable around 10-15 mm. Pellets are almost exclusively made from wood sawdust and have been developed relatively recently as an alternative to fossil fuels such as natural gas and heating oil. Their size is such that they can be conveniently blown from a tanker to a storage silo and they can be fed to a burner by a simple auger feeding. A broad range of pellet stoves, central heating furnaces, and other heating appliances have been developed recently.
Ingot or puck briquetting systems provide flexibility and advantages with respect to pellet plants. Ingot or puck briquetting systems accept a wider range of feedstock, which is especially useful when wood sawdust feedstock is scarce. Ingot or puck briquetting feed stock particle size does not need to be ground as fine as pellet operations and they are more tolerant with respect to humidity content. Pellets are more expensive to produce than briquettes and excessive handling causes them to degrade and become dustier. The extreme pressures used in pelletizing systems (1.7 GPa) causes wear and parts such as dies need replacing regularly. This can represent a significant operating cost. Periodic, replacement of motor drives within pellet mills is also common. Because of their larger surface to volume ratio, pellets need to be kept dry and can only be stored for a relatively short period of time. Moreover, pelletizing of materials containing contaminants such as lime, clay and/or other low temperature melting point constituents is a severe operational production limitation. The high operating temperatures cause the material to liquefy and plug the orifice of the pellet press dies. For the most part pelletizing is applied to woody biomass waste and they are not suitable for agro-food waste or other types of waste.
The majority of the high throughput (>500 kg/hr), industrial briquette presses require high capital acquisition costs, are constructed from costly proprietary components and are subject to high operational and maintenance fees.
The prior art systems and method for the generation of densified logs or briquettes from various fiber materials have many drawbacks